The present invention relates to novel treatment of gas, more particularly, to a process for treating gas, e.g., exhaust gas containing organic gas such as an organic solvent and the like, preferably by bringing it into contact with liquid containing active sludge or the like under specified conditions to decompose it, or to remove it by other methods.
There have been known various processes for destructive treatment of, e.g., exhaust gas containing an organic solvent such as a direct burning process, burning using media of a heat-accumulating type (heat-accumulating burning method) or an absorption method in which useful components are absorbed for recovery using activated carbon and the like as an absorbant.
Though not directed to the organic solvent, a microorganism-utilizing process is known for deodorizing sewage and the like. For example, JP-A-5-123527/1993 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an unexamined xe2x80x9cJapanese Patent Kokai Publicationxe2x80x9d) discloses a process for deodorizing effectively odored exhaust gas by applying residual sludge (activated).
However, in the course of the investigations toward the present invention the following problems have been encountered. Namely, among the aforementioned conventional processes, the direct burning process has such a drawback that it is expensive. The heat-accumulating burning method requires the addition of auxiliary fuel in case of applying this method under the condition of a high gas concentration to an extent of exceeding 500 ppm. Accordingly, its running cost is high. The method using the active sludge is applied now for deodorizing sewage and the like, however, its effectiveness is in question when applied for treating exhaust gas containing an organic gas such as vapor of an organic solvent such as methyl alcohol and ethyl alcohol. To this end, the treatment of exhaust gas using the active sludge is not generally put into practice.
Under such circumstances as mentioned above, the development of a novel practical process is required now which is excellent in treating effectively, simply and industrially the exhaust gas containing organic gas at low costs.
It is an object of the present invention to solve the above problems and provide an excellent treatment process of organic gas, especially, microbial treatment process of organic gas using active sludge and the like.
Further objects of the present invention will become apparent in the entire disclosure.
The present inventors studied assiduously to solve the above problems and attain the purpose of the present invention. As a result, it has been found that a target gas such as organic gas and the like can be treated very effectively by changing the flow rate ratio of the gas to the liquid with time in bringing a gas to be treated into contact with a liquid capable of treating the gas in a tower (or column) to decompose or remove the gas dissolved in the liquid. The present invention has been completed on the basis of the above findings.
In other words, according to a first aspect of the present invention, there is provided a process for treating a gas including the step of bringing a gas to be treated into contact with a liquid capable of treating the gas in a gas-treatment tower to decompose or remove the gas dissolved in the liquid while the flow rate ratio of the gas to the liquid is controlled so as to be appropriately changed versus time.
The tower may be a treatment tower, in which gas and liquid components are effectively brought into contact with each other to dissolve a target gas component into the liquid, i.e., which is capable of making gas-liquid contact effectively.
The first aspect of the invention includes the following embodiments:
1-1. the process in which the tower is a plate tower having, e.g., perforated plates etc. inside of the tower or a packed bed tower containing fillers in the tower;
1-2. the process in which the flow rate ratio is changed periodically to form a trigonometric function wave (e.g., sinusoidal, cosine, cosecant or cotangent function wave) or a composed wave of these waves; and
1-3. the process in which the liquid for treating the gas comprises a liquid containing active sludge or microorganisms capable of activating sludge.
The preferred embodiments of the present invention includes the following processes:
1a. A process for treating gas including the steps of using a gas-treatment tower such as a plate tower having, e.g., perforated plates disposed inside of the tower, packed bed tower containing fillers in the tower and the like, feeding a gas to be treated and a liquid capable of treating the gas into the tower to provide gas-liquid contact to decompose or remove a target gas while the flow rate ratio of the gas to the liquid is changed with time.
1b. in the process 1a, the flow rate ratio is changed periodically to form a trigonometric wave (or waves) or a composed wave thereof; and
1c. in the 1a process, the liquid comprises a liquid containing active sludge or microorganisms capable of living in the activating sludge liquid. Preferably, a liquid comprising microorganisms living in an activating sludge is used, said microorganisms being ones existing in a liquid for the active sludge-treatment.
The present inventors studied assiduously to solve the above problems and attain the purpose of the present invention. As a result, it has been found that a gas component contained in a treating liquid can be treated very effectively, e.g., decomposed, or the like, by applying microbial treatment or other treatment in the following way. Namely, one part of gas to be treated is rendered to flow up in a gas treatment tower. At the same time, the other part of the gas is branched and mixed with a liquid capable of treating the gas and allowed to flow down together with the liquid into the tower. Thus, both the parts of the gas are flown in opposing directions each other and brought into contact with the liquid in the tower. The present invention has been completed on the basis of the above findings.
In other words, according to the second aspect of the present invention there is provided a process for treating gas wherein a part of the gas to be treated is allowed to flow up in the gas treatment tower to perform gas/liquid contact, while the residual part of the gas is allowed to flow down in the tower together with a descending liquid to perform gas/liquid contact, thereby, bringing both the parts of the gas into contact with the liquid in the tower, to decompose or remove the target gas component contained in the liquid.
The tower may be a treatment tower, in which the gas and liquid components are effectively brought into contact with each other to dissolve the target gas component into the liquid, i.e., which is capable of performing gas-liquid contact effectively. Usually, the liquid is allowed to flow down. On the contrary, the gas is allowed to flow up from the bottom of the tower. Both of the liquid and the gas are brought into contact with each other to dissolve the target gas component of the gas into the liquid.
The second aspect of the invention includes the following embodiments.
2-1. The process in which the tower is a plate-stacked tower having perforated plates inside of the tower or a packed bed tower containing fillers in the tower. Preferably, feeding gas/liquid contact in the tower.
2-2. The process in which another part of the gas (branched gas) is fed in the midway of a pipe for feeding the liquid into the tower, e.g., the plate tower.
In this case, the mixing state of the liquid and the gas changes depending on kind and volume of the gas component(s), mixing process, time required for the mixture to travel from the mixing point to the top of the tower, temperatures of the liquid and the gas, etc. Usually, the fed gas (branched gas) is introduced into the tower while keeping such states that one part of the gas is homogeneously contained (dissolved) in the liquid and that the residual part of the gas is almost homogeneously mixed. This premixing is preferable, since it enables the liquid to perform preparatorily good contact with the gas. It is especially preferable that mixing is designed so as to dissolve most of the target gas component(s) to be treated into the liquid.
2-3. The process in which the gas dissolved in the liquid is decomposed and treated by a microbial treatment.
Various processes may be applied for decomposing or removing the target gas component irrespective of whether these processes are known or will be developed in the future. Among them, microbial treatment is preferable because it is applicable to the treatment of many kinds of gas components. Further, it can be done simply at low costs.
2-4. The process in which the liquid comprises a liquid for the active sludge treatment or a liquid containing microorganisms existing, or being capable of being used, in a liquid for activating sludge treatment.
The second aspect of the present invention includes the following preferred embodiments.
2a. A treatment for decomposing gas by feeding a gas to be treated and a liquid capable of treating the gas into a gas-treatment tower, which includes a plate tower having perforated plates stacked or laminated inside of the tower and packed bed tower containing fillers in the tower, to perform gas-liquid contact and decompose the gas on the condition that one part of the gas (branched gas) is fed into a path of a feed pipe of the liquid connected to the tower, preferably, to the plate tower.
2b. The process (2a) in which the liquid is a liquid for the active sludge treatment or a liquid containing microorganisms existing, or being capable of being used, in a liquid for activating sludge treatment.